This safety device is designed to prevent a person outside the vehicle or in transit who is touching a metal part from exposure to a potentially dangerous electrical charge.
The danger of exposing passengers on public transportation vehicles to electrical shock has been the object of many regulations and codes.
Moreover, manufacturers of electrically propelled public transportation vehicles have provided safety equipment to decrease risk of electric shock and have conducted numerous experiments to control electrical insulation at various levels and on different units with which passengers are likely to come into contact.
There are many measures that can be taken to protect passengers from electrical shock. It is possible to use insulating coverings, for example, polyester or fiberglass epoxy, on all metal parts of the vehicle. The vehicle floor may be covered with an insulating material. Another customary practice is to electrically insulate metal devices and accessories such as doors, support bars, steps, and the like from the vehicle when they are installed. However, all these safety measures do not eliminate the danger of electrical shock to passengers and at best, merely reduce the rate of occurrence.